Titanium(IV)-chelates in which, for example, acetylacetone is used as the chelate former are known. These titanium acetylacetone-chelates, which are also known as titanium acetylacetonates, are commonly used as additives for flexographic printing inks based on nitrocellulose or cellulose ester derivatives. The cross-linking effects of the titanium component in these chelates is reduced to such an extent that no cross-linking occurs in the printing ink itself; the cross-linking effect occurs only after imprinting of the substrate upon evaporation of the solvent and under the influence of humidity.
However, the titanium acetylacetonates exhibit the following disadvantages when they are used in the above-mentioned printing inks:
Because of their intense reddish brown color, they impart a yellowish tinge to white printing inks. In addition, upon drying on the substrate they often develop an undesirable odor. Furthermore, the above-mentioned discoloration occurs especially in the case of those substrate materials which contain antioxidants based on phenol. Such antioxidants are, for example, contained in polyolefin foils or in heat-sealing substrates, so that printing inks containing titanium acetylacetonates cannot be employed for imprinting such materials without discoloration of the substrate.